Summary The Bell 206L-3, registration C-GDTM, serial number51366, operated by HliStar Inc., was on a visual flight rules flight from LaTuque, Quebec, to Val-d'Or, Quebec. Approximately 20minutes after take-off, at about 0810 eastern daylight time and at 2000feet above sea level, the needle on the engine oil pressure gauge started to fluctuate. As a precaution, the pilot landed the aircraft in a marsh and shut down the engine. After conducting a pre-flight inspection, the pilot started the engine and took off with the intention of landing on a road one kilometre away. Just before the helicopter reached the road, there was a fluctuation in the engine oil pressure and engine torque. Right after that, there was an explosion and the engine stopped. The pilot did an autorotation that ended with a hard landing on the road. The helicopter was heavily damaged. The pilot was alone on board and was not injured. Ce rapport est galement disponible en franais. Other Factual Information On the morning of the accident, the pilot carried out a pre-flight inspection of the helicopter. No oil leaks were observed and the oil level in the tank was within the allowable limits. The pilot was alone on board and took off from LaTuque Airport, Quebec, around 0750 eastern daylight time1 for Val-d'Or Airport, Quebec, where the helicopter was to undergo a 100-hour inspection. The weather conditions were favourable and the flight was conducted in accordance with visual flight rules. About 20 minutes after departure, the needle in the engine oil pressure gauge was observed to be fluctuating within the limits. The engine oil temperature was normal, there were no other abnormal conditions, and the engine chip detector light was not on. The pilot decided to land in the nearest area he felt was safe. The pilot landed the helicopter in a mosquito-infested marsh about one kilometre from a road he had just flown over. After shutting down the engine, an unusual amount of bluish smoke was observed coming out of the exhaust pipe. A quick inspection of the engine compartment revealed no oil leaks or damage. The pilot called Val-d'Or and spoke with an aircraft maintenance engineer (AME) working for the company responsible for maintaining the aircraft. The AME recommended checking that there were no oil leaks in the engine compartment and that the oil was at an appropriate level. The AME also asked the pilot to do an engine run-up before contacting him again. The pilot did the checks and then started up the helicopter. Bluish smoke was still coming out of the exhaust pipe; however, the engine oil pressure was stable, in the lower limits of the gauge. The pilot did an engine run-up for some time, and then hovered. Rather than contacting the AME as agreed, the pilot headed to the adjacent road after concluding that the engine oil pressure gauge was defective. At about 50 feet above the road, the engine oil pressure gauge needle and the engine torque indicator needle began fluctuating. Right after that, there was an explosion and the engine failed. The pilot entered an autorotation, and on landing, the rear part of the skids touched the ground and the nose of the helicopter tipped forward. The main rotor cut off the tail boom, and the helicopter came to rest about 30feet from that point. Shortly thereafter, the pilot notified search and rescue by satellite telephone. The pilot was certified and qualified for the flight in accordance with existing regulations. He owned HliStar Inc. since December1997. He had about 5800flying hours on helicopters, including 780hours on type. On 08December2005, he had passed the pilot proficiency check flight test. The aircraft was registered for commercial use and its certificate of airworthiness was valid. The aircraft was maintained and operated in accordance with existing procedures and regulations. The helicopter was equipped with an emergency locator transmitter (ELT), Pointer Sentry, model400010, which activated at impact. Figure1.- Engine oil pressure and temperature gauge (extract from the flight manual, section 1) The Bell 206L-3 has a gauge that allows the pilot to determine the status of the engine oil system (see Figure1). It shows the engine oil pressure and temperature. However, there is no caution light to warn of low engine oil pressure or high engine oil temperature. When an abnormal condition occurs, the pilot must determine how serious it is based on the engine oil temperature and pressure. The pilot must then follow the appropriate procedure recommended in the helicopter's flight manual. Engine oil pressure outside the prescribed limits indicates either a fault in the engine oil circulation system, a low engine oil level, or a system indication problem. Since the engine oil temperature sensor is located directly at the oil tank outlet, it is possible for the oil temperature to indicate normal even when the oil level is low. Three limiting ranges for engine oil pressure are defined according to the rpm of the engine's low-pressure compressor (N1RPM), with N1 being proportional to the engine power delivered. Section 3-13 of the Bell Helicopter flight manual (see Figure2) stipulates that, when engine oil pressure is below the minimum or above the maximum, the pilot must land as soon as possible. This means that it is recommended that the pilot land without delay at the nearest suitable area that allows a safe approach and landing. Figure2. Extracts from the Bell 206L-3 flight manual However, if engine oil pressure fluctuates without exceeding the limits, the pilot must monitor the engine oil pressure and temperature, and land as soon as practicable. In such a situation, the landing site and flight duration are at the pilot's discretion. Extended flight beyond the nearest approved landing area is not recommended. Section 3-14 of the manual stipulates that, when engine oil temperature exceeds the allowable limit, the pilot must land as soon as possible. The Rolls-Royce 250 C-30P engine, serial number CAE895434, had accumulated 1590.5hours since its last overhaul. The oil system includes a pressure pump and four scavenge pumps; they are all located inside the accessory drive gearbox. The Rolls-Royce engine has nine main bearings numbered 1through8. The third bearing is numbered2. The aircraft had flown for about 15hours since the last time oil had been added. The oil consumption could not be precisely determined because it had not been entered in the aircraft logbook, and it was not required to be by the Canadian regulation. However, Section8 of the Rotorcraft Flight Manual (RFM) requests that an appropriate entry be made in the helicopter logbook when oil has been added to the engine, transmission, or tail rotor gearbox. According to the information gathered, oil consumption was approximately one litre per 100hours, which is within the manufacturer's oil consumption limit for the C-30 engine. No significant changes had been observed since the last 100-hour inspection. After the aircraft was imported into Canada in May2004, the operator had observed that the engine emitted slightly bluish smoke on start-up. A change in the brand of oil being used remedied the problem. Bluish smoke coming from exhaust pipes is usually a sign that engine oil is entering the power turbine section of the engine and is being burnt due to the high temperatures within this section. The engine was torn down at the TSB Engineering Laboratory. Examination of the controls and external lines of the engine did not identify any anomalies. A large amount of carbon deposits had accumulated in the accessory drive gearbox and in the power turbine section. Bearings 6and 7,composed of iron and silver, were destroyed. The area adjacent to bearings 6and 7had overheated and exceeded a temperature of 900C.2 Oil residue found in the external tank of the oil sump suggested that bearings 6and 7had been lubricated at the time they disintegrated. Because of the major damage to bearings 6and 7,it was not possible to determine the cause of their failure. The high internal temperature of more than 900C melted the turbine compressor connection tie bolt, resulting in an overspeed and a disconnection that caused turbine wheel number1 to disintegrate. The number 8bearing sump nut had multiple dents where the fractured tie bolt made contact. According to Rolls-Royce, a lack of lubrication first causes bearing8 to fail. Bearing8 was not lacking oil, but it was on the verge of failing. None of the bearing components showed any evidence of severe thermal distress that would suggest that the No.8 bearing had operated without oil. The two magnetic chip detectors located on the accessory drive gearbox showed no chips. Two oil samples were taken; one from the engine and one from the oil tank. Analysis of the samples established that they contained twice as much iron and eight times as much silver as new oil.